The proposed research examines the role of lateral inhibition in studies of metacontrast. A number of theories have been posited to explain metacontrast and each has used the notion of lateral inhibition. Each of these theories are, however, open to some kind of methodological criticism. The proposed experiments provide a test of those theories. In addition to testing the theories the proposed experiments more carefully examine the general concept of lateral inhibition and whether its use in general is a meaningful one. To accomplish these ends the experiments use a spatial forced choice technique with a black disk being surrounded by one of two black rings. With the disk size held constant both the ring width and the intercontour distance are manipulated independently. A third variable is the duration of the masking rings. The three variables were chosen because they maximize or minimize the extent of metacontrast and should according to some theories have dramatic effects on the shape of the metacontrast functions obtained. These experiments not only test two specific theories of metacontrast, they examine the concept of lateral inhibition with indirect measures on human subjects with a suprathreshold task, and last, they provide useful parametric data in an area that needs further investigation.